Plasma treated thermal CVD of TaN films from tantalum halide precursors

ABSTRACT

A plasma treated chemical vapor deposition (PTTCVD) method for depositing high quality conformal tantalum nitride (TaN x ) films from inorganic tantalum halide (TaX 5 ) precursors and a nitrogen containing gas is described. The inorganic tantalum halide precursors are tantalum pentafluoride (TaF 5 ), tantalum pentachloride (TaCl 5 ) and tantalum pentabromide (TaBr 5 ). In a thermal CVD process, a TaX 5  vapor is delivered into a heated chamber. The vapor is combined with a process gas containing nitrogen to deposit a TaN x  film on a substrate that is heated to 300° C.-500° C. A hydrogen gas is introduced in a radiofrequency generated plasma to plasma treat the TaN x  film. The plasma treatment is performed periodically until a desired TaN x  film thickness is achieved. The PTTCVD films have improved microstructure and reduced resistivity with no change in step coverage. The deposited TaN x  film is useful for integrated circuits containing copper films, especially in small high aspect ratio features. The high conformality of these films is superior to films deposited by PVD.

FIELD OF THE INVENTION

The invention relates to the formation of integrated circuits, andspecifically to chemical vapor deposition of tantalum nitride films fromtantalum halide precursors.

BACKGROUND

Integrated circuits (IC) provide the pathways for signal transport in anelectrical device. An IC in a device is composed of a number of activetransistors contained in a silicon base layer of a semiconductorsubstrate. To increase the capacity of an IC, large numbers ofinterconnections with metal “wires” are made between one activetransistor in the silicon base of the substrate and another activetransistor in the silicon base of the substrate. The interconnections,collectively known as the metal interconnection of a circuit, are madethrough holes, vias or trenches that are cut into a substrate. Theparticular point of the metal interconnection which actually makescontact with the silicon base is known as the contact. The remainder ofthe hole, via or trench is filled with a conductive material, termed acontact plug. As transistor densities continue to increase, forminghigher level integrated circuits, the diameter of the contact plug mustdecrease to allow for the increased number of interconnections,multilevel metalization structures and higher aspect ratio vias.

Aluminum has been the accepted standard for contacts andinterconnections in integrated circuits. However, problems with aluminumelectromigration and its high electrical resistivity require newmaterials for newer structures having submicron dimensions. Copper holdspromise as the interconnect material for the next generation ofintegrated circuits in ultra large scale integration (ULSI) circuitry,yet the formation of copper silicide (Cu—Si) compounds at lowtemperatures and its electromigration through a silicon oxide (SiO₂)layer are disadvantages to its use.

As the shift occurs from aluminum to copper as an interconnect elementof choice, new materials are required to serve as a barrier, preventingcopper diffusion into the underlying dielectric layers of the substrateand to form an effective “glue” layer for subsequent copper deposition.New materials are also required to serve as a liner, adheringsubsequently deposited copper to the substrate. The liner must alsoprovide a low electrical resistance interface between copper and thebarrier material. Barrier layers that were previously used withaluminum, such as titanium (Ti) and titanium nitride (TiN) barrierlayers deposited either by physical vapor deposition (PVD) such assputtering and/or chemical vapor deposition (CVD), are ineffective asdiffusion barriers to copper. In addition, Ti reacts with copper to formcopper titanium compounds at the relatively low temperatures used withPVD and/or CVD.

Sputtered tantalum (Ta) and reactive sputtered tantalum nitride (TaN)have been demonstrated to be good diffusion barriers between copper anda silicon substrate due to their high conductivity, high thermalstability and resistance to diffusion of foreign atoms. However, thedeposited Ta and/or TaN film has inherently poor step coverage due toits shadowing effects. Thus the sputtering process is limited torelatively large feature sizes (>0.3 μm) and small aspect ratio contactsand vias. CVD offers the inherent advantage over PVD of betterconformality, even in small structures (<0.25 μm) with high aspectratios. However, CVD of Ta and TaN with metal-organic sources such astertbutylimidotris(diethylamido)tantalum (TBTDET), pentakis(dimethylamino) tantalum (PDMAT) and pentakis (diethylanmino) tantalum(PDEAT) yields mixed results. Additional problems are that all resultingfilms have relatively high concentrations of oxygen and carbonimpurities and require the use of a carrier gas.

The need to use a carrier gas presents the disadvantage that theconcentration of the precursor gas in the carrier is not preciselyknown. As a result, accurate metering of a mixture of a carrier gas anda precursor gas to the CVD reaction chamber does not insure accuratemetering of the precursor gas alone to the reactor. This can cause thereactants in the CVD chamber to be either too rich or too lean. The useof a carrier gas also presents the disadvantage that particulates arefrequently picked up by the flowing carrier gas and delivered ascontaminants to the CVD reaction chamber. Particulates on the surface ofa semiconductor wafer during processing can result in the production ofdefective semiconductor devices.

Thus, a process to deposit TaN at the relatively low temperatures usedin PECVD (<500° C.) would provide an advantage in the formation ofcopper barriers for the next generation of IC. Ideally, the depositedfilm will have a high step coverage (the ratio of the coating thicknessat the bottom of a feature to the thickness on the sides of a feature oron the top surface of the substrate or wafer adjacent the feature), gooddiffusion barrier properties, minimal impurities, low resistivity, goodconformality (even coverage of complex topography of high aspect ratiofeatures), and ideally the process will have a high deposition rate.

SUMMARY OF THE INVENTION

The invention is directed to a method of depositing a tantalum nitride(TaN_(x)) film from a tantalum halide precursor on a substrate. Thetantalum halide precursor is delivered at a temperature sufficient tovaporize the precursor to provide a vaporization pressure to deliver thetantalum vapor to a reaction chamber containing the substrate. Thevaporization pressure is greater than about 3 Torr. The vapor iscombined with a process gas containing nitrogen and TaN_(x) is depositedon the substrate by a thermal chemical vapor deposition (thermal CVD)process. The deposition is halted to plasma treat the film surface, thendeposition is resumed. The plasma treatments are performed at regularintervals in the thermal CVD process (PTTCVD) until a desired filmthickness is obtained. The tantalum halide precursor is tantalumfluoride (TaF), tantalum chloride (TaCl) or tantalum bromide (TaBr),preferably tantalum pentafluoride (TaF₅), tantalum pentachloride (TaCl₅)or tantalum pentabromide (TaBr₅). The substrate temperature is in therange of about 300° C.-500° C.

The invention is also directed to a method of depositing a TaN_(x) filmfrom a TaF₅ or TaCl₅ precursor on a substrate by elevating the precursortemperature sufficient to vaporize the precursor to provide a pressureto deliver the vapor. The vapor is combined with a process gascontaining nitrogen and TaN_(x) is deposited on the substrate by athermal chemical vapor deposition (thermal CVD) process. The depositionis halted to plasma treat the film surface, then deposition is resumed.The plasma treatments are performed at regular intervals in the thermalCVD process until a desired film thickness is obtained.

The invention is further directed to method of depositing a TaN_(x) filmfrom a TaBr₅ precursor on a substrate without a carrier gas. Thetemperature of the precursor is elevated sufficient to produce atantalum vapor. The vapor is combined with a process gas containingnitrogen and TaN_(x) is deposited on the substrate by a thermal chemicalvapor deposition (thermal CVD) process. The deposition is halted toplasma treat the film surface, then deposition is resumed. The plasmatreatments are performed at regular intervals in the thermal CVD processuntil a desired film thickness is obtained.

The invention is still further directed to a substrate integral with acopper (Cu) layer and a TaN_(x) layer in which diffusion of Cu isprevented by the TaN_(x) layer.

The TaN_(x) layer deposited by plasma treated thermal CVD according tothe invention has minimal impurities and low resistivity. The filmprovides good step coverage, good conformality in high aspect ratiofeatures and is a good diffusion barrier to a copper film.

It will be appreciated that the disclosed method and substrates of theinvention have an array of applications. These and other advantages willbe further understood with reference to the following drawings anddetailed description.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic of an apparatus for plasma treated thermalchemical vapor deposition (PTTCVD).

FIG. 2 is a graph of vapor pressure versus temperature for tantalumhalides.

FIG. 3 is a photograph of a scanning electron micrograph (SEM) of atantalum nitride (TaN_(x)) film deposited using a tantalum pentafluoride(TaF₅) precursor deposited by thermal chemical vapor deposition (CVD).

FIG. 4 is a photograph of a SEM of a TaN_(x) film deposited using a TaF₅precursor deposited by plasma treated thermal CVD (PTTCVD).

FIG. 5 is a photograph of a SEM of a TaN_(x) film deposited using atantalum pentabromide (TaBr₅) precursor deposited by thermal CVD.

FIG. 6 is a photograph of a SEM of a TaN_(x) film deposited using aTaBr₅ precursor deposited by PTTCVD.

FIG. 7 is an Auger spectrum tracing of a TaN_(x) film deposited bythermal CVD using a TaBr₅ precursor deposited on a Cu/TiN/Si stack.

DETAILED DESCRIPTION

Refractory transition metals such as tantalum (Ta) and their nitridefilms (TaN) are effective diffusion barriers to copper (Cu). Theireffectiveness is due to their high thermal stability, high conductivityand resistance to diffusion of foreign elements or impurities. Ta andTaN are especially attractive due to their chemical inertness with Cu;no compounds form between Cu and Ta or Cu and N.

Tantalum halides provide a convenient inorganic source for Ta and TaN.Specifically, the inorganic precursor is a tantalum pentahalide (TaX₅)where X represents the halides fluorine (F), chlorine (Cl) and bromine(Br). Table 1 shows relevant thermodynamic properties of the tantalumhalide precursors, specifically tantalum pentafluoride (TaF₅), tantalumpentachloride (TaCl₅) and tantalum bromide (TaBr₅), with tantalumpentaiodide (Tal₅) included for comparison. The TaF₅, TaCl₅ and TaBr₅precursor materials are all solids at room temperature (18° C.-22° C.).

TABLE 1 MELTING BOILING CHANGE IN HEAT OF PRECURSOR POINT POINTFORMATION (ΔHf) TaF₅  97° C. 230° C. −455 kcal/mole TaCl₅ 216° C. 242°C. −205 kcal/mole TaBr₅ 265° C. 349° C. −143 kcal/mole Tal₅ 367° C. 397°C.  −82 kcal/mole

In chemical vapor deposition (CVD) processes, gas precursors areactivated using either thermal energy or electrical energy. Uponactivation, the gas precursors react chemically to form a film. Apreferred method of CVD is illustrated in FIG. 1 and is disclosed in acopending application entitled APPARATUS AND METHODS FOR DELIVERY OFVAPOR FROM SOLID SOURCES TO A CVD CHAMBER by Westendorp et al. filed onthe same date as the present application and assigned to Tokyo ElectronLimited and incorporated by reference herein in its entirety. A chemicalvapor deposition (CVD) system 10 includes a CVD reaction chamber 11 anda precursor delivery system 12. In the reaction chamber, a reaction iscarried out to convert a precursor gas of, for example, tantalumchloride (TaCl) or other tantalum halide compound, into a film such as abarrier layer film of tantalum (Ta) or tantalum nitride (TaN). The TaNfilm is not limited to any particular stoichiometry (TaN_(x)), sinceTaN_(x) can be continuously varied by changing the ratio of gases in anygiven deposition. Thus, as used herein, TaN_(x) encompasses a tantalumnitride film of any stoichiometry.

The precursor delivery system 12 includes a source 13 of precursor gashaving a gas outlet 14, which communicates through a metering system 15with a gas inlet 16 to the CVD reaction chamber 11. The source 13generates a precursor gas, for example a tantalum halide vapor, from atantalum halide compound. The compound is one that is in a solid statewhen at standard temperature and pressure. The precursor source ismaintained, preferably by controlled heating, at a temperature that willproduce a desired vapor pressure of precursor. Preferably, the vaporpressure is one that is itself sufficient to deliver the precursor vaporto the reaction chamber, preferably without the use of a carrier gas.The metering system 15 maintains a flow of the precursor gas vapor fromthe source 13 into the reaction chamber at a rate that is sufficient tomaintain a commercially viable CVD process in the reaction chamber.

The reaction chamber 11 is a generally conventional CVD reactor andincludes a vacuum chamber 20 that is bounded by a vacuum tight chamberwall 21. In the chamber 20 is situated a substrate support or susceptor22 on which a substrate such as a semiconductor wafer 23 is supported.The chamber 20 is maintained at a vacuum appropriate for the performanceof a CVD reaction that will deposit a film such as a Ta/TaN_(x) barrierlayer on the semiconductor wafer substrate 23. A preferred pressurerange for the CVD reaction chamber 11 is in the range of from 0.2 to 5.0Torr. The vacuum is maintained by controlled operation of a vacuum pump24 and of inlet gas sources 25 that include the delivery system 12 andmay also include reducing gas sources 26 of, for example, hydrogen (H₂),nitrogen (N₂) or ammonia (NH₃) for use in carrying out a tantalumreduction reaction, and an inert gas source 27 for a gas such as argon(Ar) or helium (He). The gases from the sources 25 enter the chamber 20through a showerhead 28 that is situated at one end of the chamber 20opposite the substrate 23, generally parallel to and facing thesubstrate 23.

The precursor gas source 13 includes a sealed evaporator 30 thatincludes a cylindrical evaporation vessel 31 having a verticallyoriented axis 32. The vessel 31 is bounded by a cylindrical wall 33formed of a high temperature tolerant and non-corrosive material such asthe alloy INCONEL 600, the inside surface 34 of which is highly polishedand smooth. The wall 33 has a flat circular closed bottom 35 and an opentop, which is sealed by a cover 36 of the same heat tolerant andnon-corrosive material as the wall 33. The outlet 14 of the source 13 issituated in the cover 36. When high temperatures are used, such as withTil₄ or TaBr₅, the cover 36 is sealed to a flange ring 37 that isintegral to the top of the wall 33 by a high temperature tolerant vacuumcompatible metal seal 38 such as a HELICOFLEX seal, which is formed of aC-shaped nickel tube surrounding an INCONEL coil spring. With materialsrequiring lower temperatures, such as, TaCl₅ and TaF₅, a conventionalelastomeric O-ring seal may be used to seal the cover.

Connected to the vessel 31 through the cover 36 is a source 39 of acarrier gas, which is preferably an inert gas such as He or Ar. Thesource 13 includes a mass of precursor material such as tantalumfluoride, chloride or bromide (TaX), preferably as the pentahalide(TaX₅), at the bottom of the vessel 31, which is loaded into the vessel31 at standard temperature and pressure in a solid state. The vessel 31is filled with tantalum halide vapor by sealing the chamber with thesolid mass of Ta_(X) therein. The halide is supplied as a precursor mass40 that is placed at the bottom of the vessel 31, where it is heated,preferably to a liquid state as long as the resulting vapor pressure isin an acceptable range. Where the mass 40 is liquid, the vapor liesabove the level of the liquid mass 40. Because wall 33 is a verticalcylinder, the surface area of TaX mass 40, if a liquid, remains constantregardless of the level of depletion of the TaX.

The delivery system 12 is not limited to direct delivery of a precursor40 but can be used in the alternative for delivery of precursor 40 alongwith a carrier gas, which can be introduced into the vessel 31 from gassource 39. Such a gas may be hydrogen (H₂) or an inert gas such ashelium (He) or argon (Ar). Where a carrier gas is used, it may beintroduced into the vessel 31 so as to distribute across the top surfaceof the precursor mass 40 or may be introduced into the vessel 31 so asto percolate through the mass 40 from the bottom 35 of the vessel 31with upward diffusion in order to achieve maximum surface area exposureof the mass 40 to the carrier gas. Yet another alternative is tovaporize a liquid that is in the vessel 31. However, such alternativesadd undesired particulates and do not provide the controlled deliveryrate achieved by the direct delivery of the precursor, that is, deliverywithout the use of a carrier gas. Therefore, direct delivery of theprecursor is preferred.

To maintain the temperature of the precursor 40 in the vessel 31, thebottom 35 of the wall 33 is maintained in thermal communication with aheater 44, which maintains the precursor 40 at a controlled temperature,preferably above its melting point, that will produce a vapor pressuregreater than about 3 Torr in the absence of a carrier gas (i.e., adirect delivery system), and a lower vapor pressure such as about 1 Torrwhen a carrier gas is used. The exact vapor pressure depends upon othervariables such as the quantity of carrier gas the surface area of thesubstrate and so on. In a direct system for tantalum, a vapor pressurecan be maintained at the preferred pressure of 5 Torr or above byheating the a tantalum halide precursor in the 95° C. to 205° C. rangeas shown in FIG. 2. For TaX₅ the desired temperature is at least about95° C. for TaF₅, the desired temperature is at least about 145° C. forTaCl₅, and the desired temperature is at least about 205° C. for TaBr₅.The melting points of the respective fluoride, chloride and bromidetantalum pentahalide compounds are in the 97° C. to 265° C. range. Amuch higher temperature is required for tantalum pentaiodide (Tal₅) toproduce a sufficient vapor pressure in the vessel 31. Temperaturesshould not be so high as to cause premature reaction of the gases in theshowerhead 28 or otherwise before contacting the wafer 23.

For purposes of example, a temperature of 180° C. is assumed to be thecontrol temperature for the heating of the bottom 35 of the vessel 31.This temperature is appropriate for producing a desired vapor pressurewith a titanium tetraiodide (Til₄) precursor. Given this temperature atthe bottom 35 of the vessel 31, to prevent condensation of the precursorvapor on the walls 33 and cover 36 of the vessel 31, the cover ismaintained at a higher temperature than the heater 44 at the bottom 35of the wall 33 of, for example, 190° C., by a separately controlledheater 45 that is in thermal contact with the outside of the cover 36.The sides of the chamber wall 33 are surrounded by an annular trappedair space 46, which is contained between the chamber wall 33 and asurrounding concentric outer aluminum wall or can 47. The can 47 isfurther surrounded by an annular layer of silicon foam insulation 48.This temperature maintaining arrangement maintains the vapor in a volumeof the vessel 31 bounded by the cover 36, the sides of the walls 33 andthe surface 42 of the precursor mass 40 in the desired exampletemperature range of between 180° C. and 190° C. and the pressuregreater than about 3 Torr, preferably at greater than 5 Torr. Thetemperature that is appropriate to maintain the desired pressure willvary with the precursor material, which is primarily contemplated as abeing tantalum or titanium halide compound.

The vapor flow metering system 15 includes a delivery tube 50 of atleast ½ inch in diameter, or at least 10 millimeters inside diameter,and preferably larger so as to provide no appreciable pressure drop atthe flow rate desired, which is at least approximately 2 to 40 standardcubic centimeters per minute (sccm). The tube 50 extends from theprecursor gas source 13 to which it connects at its upstream end to theoutlet 14, to the reaction chamber to which it connects at itsdownstream end to the inlet 16. The entire length of the tube 50 fromthe evaporator outlet 14 to the reactor inlet 16 and the showerhead 28of the reactor chamber 20 are also preferably heated to above theevaporation temperature of the precursor material 40, for example, to195° C.

In the tube 50 is provided baffle plate 51 in which is centered acircular orifice 52, which preferably has a diameter of approximately0.089 inches. The pressure drop from gauge 1 56 to gauge 2 57 isregulated by control valve 53. This pressure drop after control valve 53through orifice 52 and into reaction chamber 11 is greater than about 10milliTorr and will be proportional to the flow rate. A shut-off valve 54is provided in the line 50 between the outlet 14 of the evaporator 13and the control valve 53 to close the vessel 31 of the evaporator 13.

Pressure sensors 55-58 are provided in the system 10 to provideinformation to a controller 60 for use in controlling the system 10,including controlling the flow rate of precursor gas from the deliverysystem 15 into the chamber 20 of the CVD reaction chamber. The pressuresensors include sensor 55 connected to the tube 50 between the outlet 14of the vaporator 13 and the shut-off valve 54 to monitor the pressure inthe evaporation vessel 31. A pressure sensor 56 is connected to the tube50 between the control valve 53 and the baffle 51 to monitor thepressure upstream of the orifice 52, while a pressure sensor 57 isconnected to the tube 50 between the baffle 51 and the reactor inlet 16to monitor the pressure downstream of the orifice 52. A further pressuresensor 58 is connected to the chamber 20 of the reaction chamber tomonitor the pressure in the CVD chamber 20.

Control of the flow of precursor vapor into the CVD chamber 20 of thereaction chamber is achieved by the controller 60 in response to thepressures sensed by the sensors 55-58, particularly the sensors 56 and57 which determine the pressure drop across the orifice 52. When theconditions are such that the flow of precursor vapor through the orifice52 is unchoked flow, the actual flow of precursor vapor through the tube52 is a function of the pressures monitored by pressure sensors 56 and57, and can be determined from the ratio of the pressure measured bysensor 56 on the upstream side of the orifice 52, to the pressuremeasured by sensor 57 on the downstream side of the orifice 52.

When the conditions are such that the flow of precursor vapor throughthe orifice 52 is choked flow, the actual flow of precursor vaporthrough the tube 52 is a function of only the pressure monitored bypressure sensor 57. In either case, the existence of choked or unchokedflow can be determined by the controller 60 by interpreting the processconditions. When the determination is made by the controller 60, theflow rate of precursor gas can be determined by the controller 60through calculation.

Preferably, accurate determination of the actual flow rate of precursorgas is calculated by retrieving flow rate data from lookup or multipliertables stored in a non-volatile memory 61 accessible by the controller60. When the actual flow rate of the precursor vapor is determined, thedesired flow rate can be maintained by a closed loop feedback control ofone or more of the variable orifice control valve 53, the CVD chamberpressure through evacuation pump 24 or control of reducing or inertgases from sources 26 and 27, or by control of the temperature and vaporpressure of the precursor gas in vessel 31 by control of heaters 44, 45.

As shown in FIG. 1, the solid TaF₅, TaCl₅ and TaBr₅ precursor material40 is sealed in a cylindrical corrosion resistant metal vessel 31 thatmaximizes the available surface area of the precursor material. Vaporfrom either TaF₅, TaCl₅ or TaBr₅ was delivered directly, that is,without the use of a carrier gas, by a high conductance delivery systeminto a reaction chamber 11. The reaction chamber 11 was heated to atemperature of at least about 100° C. to prevent condensation of vaporor deposition by-products.

The controlled direct delivery of tantalum halide vapor into thereaction chamber 11 was accomplished by heating the solid tantalumhalide precursor 40 to a temperature in the range of about 95° C.-205°C., the choice depending upon the particular precursor. The temperaturewas sufficient to vaporize the precursor 40 to provide a vapor pressureto deliver the tantalum halide vapor to the reaction chamber 11. Thus, acarrier gas was not necessary and preferably was not used. A sufficientvapor pressure was in the range of about 3-10 Torr. This pressure wasrequired to maintain a constant pressure drop across a defined orificein a high conductance delivery system while delivering up to about 50sccm tantalum halide precursor to a reaction chamber 11 operating in therange of about 0.1-2.0 Torr. The temperatures to obtain the desiredpressures in a direct delivery system were in the range of about 83°C.-95° C. and preferably about 95° C. with TaF₅, in the range of about130° C.-150° C. and preferably about 145° C. with TaCl₅, and in therange of about 202° C.-218° C. and preferably about 205° C. with TaBr₅.Under these conditions, TaF₅ is a liquid while TaCl₅ and TaBr₅ remainsolid.

FIG. 2 shows the relationship between the measured vapor pressure andtemperature for the precursors TaF₅, TaCl₅ and TaBr₅, with Tal₅ includedfor comparison. As previously stated, the desired pressure was greaterthan about 3 Torr and preferably greater than 5 Torr. Also, aspreviously stated, the vapor pressure for TaF₅, TaCl₅ and TaBr₅ wasdesirably low enough to be able to deposit tantalum in the absence of acarrier gas but yet sufficient to maintain a constant pressure dropacross a defined orifice in a high conductance delivery system and stillbe able to deliver up to 50 sscm TaX₅ to a reaction chamber 11 operatingat 0.1-2.0 Torr. The vapor pressure for Tal₅ was determined to be toolow for practical implementation in the described apparatus. For TaBr₅the open circles represent published values, while closed squares forTaBr₅, TaF₅, TaCl₅ and Tal₅ represent the inventors' experimental data.

A parallel plate RF discharge was used where the driven electrode wasthe gas delivery showerhead and the susceptor 22 or stage for the waferor substrate 23 was the RF ground. The selected TaX₅ vapor was combinedwith other process gases such as H₂ above the substrate, which had beenheated to a temperature between about 300° C.-500° C. Ar and He couldalso be used, either singularly or in combination, as process gases inaddition to H₂.

The thermal CVD is stopped at regular intervals to plasma treat the filmsurface. The flow of tantalum halide precursor gas and process gas isturned off or is directed around the reaction chamber 11 and a plasmatreatment is then performed on the surface of the film. For the plasmatreatment a parallel plate RF discharge is used where the drivenelectrode is the gas delivery showerhead and the wafer stage is the RFground. H₂ was used to plasma treat the film at a flow of 7 slm, afterwhich thermal CVD was resumed. The depositing, plasma treating andresumed depositing steps continued until the desired film thickness wasobtained. The plasma treatment of films deposited by thermal CVD, thatis, the plasma treated thermal CVD (PTTCVD) process, could decrease thefilm's electrical resistivity by a factor of greater than ten thousand.In addition, PTTCVD improves the film's morphology from a relativelyrough structure to a smooth dense film.

Process conditions for deposition of good quality PTTCVD TaN_(x) filmsare given in Table 2.

TABLE 2 Substrate Temperature 300° C.-500° C. TaX₅ temperature 95° C.(TaF₅), 145° C. (TaCl₅), 205° C. (TaBr₅) TaX₅ flow 1-50 sccm NH₃ flow0.1-10 slm H₂ flow 0.1-10 slm N₂ flow 0-10 slm Ar, He flow 0-10 slmProcess Pressure 0.2-5.0 Torr RF Power 0.1-5.0 W/cm² The TaF₅ and TaBr₅based PTTCVD TaN_(x) film properties for representative processconditions are given in Table 3.

TABLE 3 TaX₅ flow NH₃ flow Pressure Temp. # Thick/ H₂ flow RFResistivity step Halide conc Film Precursor (sccm) (slm) (Torr) (° C.)cycles cycle (slm) (Watts) (μΩcm) coverage (atomic %) TaN TaF₅ 14 0.40.2 440  0 < 1 <2 1 × 10⁷ TaN TaF₅ 14 0.4 0.2 440 10 70 7 200 3600 1 <2TaN TaF₅ 14 0.4 0.2 440 15 45 7 200 1100 1 <2 TaN TaBr₅ 20 1 1 430  0 <0.6 <2 1 × 10⁷ TaN TaBr₅ 20 1 1 430  6 105  7 200 32000  1 <2 TaN TaBr₅20 1 1 430 10 20 7 200 5800 1 <2

As shown in Table 3, the resistivities of the films that did not undergothe plasma treatment were high, greater than 1×10⁷ μωcm, which was thelimit of the measurement tool. As thinner layers of TaN_(x) filmsdeposited by thermal CVD were treated by the hydrogen RF discharge,lower resistivities were obtained. The electrical resistivity of thePTTCVD TaF₅ based film decreased from greater than 1×10⁷ μωcm in theuntreated state to 3600 μωcm when a 70 Å thick TaN_(x) film per cyclewas subjected to plasma treatment. The resistance further decreased to1100 μωcm when a 45 Å thick TaN_(x) film per cycle was subjected toplasma treatment. Similarly, the electrical resistivity of the PTTCVDTaBr₅ based film decreased from greater than 1×10⁷ μωcm for untreatedfilms to 32,000 μωcm when a 105 Å TaN_(x) film per cycle was subjectedto plasma treatment. A further decrease to 5800 μωcm was obtained when a20 Å thick TaN_(x) film per cycle was subjected to plasma treatment. ATaN_(x) film deposited using a TaCl₅ precursor would be expected toperform similarly since other TaN_(x) based films had properties thatwere effectively between TaF₅ and TaBr₅ precursors.

The H₂ plasma treatment process appeared to cause a fundamental changein the electrical and/or morphological properties of the TaN_(x) films.The resistivities were much lower than resistivities previously measuredwith TaN_(x) films deposited by either PVD or organometallic chemicalvapor deposition (OMCVD) when x>1. The microstructure of the TaN_(x)film also changed from a rough to a smooth surface with the cycleddeposition and plasma treatment.

Step coverage remained near 100% for all structures tested with aspectratios greater than 4:1 and did not appear to be influenced byimplementation of the plasma treatment. Impurity levels were estimatedto be less than 2 atomic concentration percent. Deposition ratesremained greater than 100 Å for all thermal CVD steps; however, thelength of the plasma treatment reduced the effective deposition rate toless than 100 Å per minute in some cases. Plasma treatment times in therange of between 10 seconds and 240 seconds have been evaluated. It hasbeen determined that, within this range, longer treatment times yieldfilms with lower resistivities for the material.

Copper diffusion barrier properties of the resulting TaN_(x) films areexpected to be good. One contributing factor may be the nitrogen richprocess, since this is known to improve barrier performance. Anotherfactor may be the generally amorphous structure of the material, sinceit is known that an amorphous material, defined as having a low fractionof crystalline structure, provides a better barrier.

Selected photographs of films deposited by both thermal CVD and PTTCVDaccording to the invention and analyzed by scanning electron microscopy(SEM) are shown in FIGS. 3-6. FIGS. 3 and 4 represent TaN_(x) filmsusing TaF₅ precursors, deposited by either thermal CVD (FIG. 3) orPTTCVD (FIG. 4). FIGS. 5 and 6 represent TaN_(x) films using TaBr₅precursors, deposited by either thermal CVD (FIG. 5) or PTTCVD (FIG. 6).Each of the figures shows a 3:1 aspect ratio structure withrepresentative bottom step coverage and side wall coverage for therespective precursors. The step coverage represents the film thicknesson the bottom of the feature divided by the film thickness on thesurface of the substrate adjacent the feature, also called the field. Anideal step coverage is 1.0 or 100%, representing identical thickness onthe bottom as on the field.

The effect of the plasma treatment was most striking on both themicrostructural and electrical properties of TaN_(x) films depositedusing TaF₅ precursors. As shown in FIGS. 3 and 4 and from Table 3, theTaF₅ precursor film had a step coverage of 1.0 (100%). The filmsgenerally appeared to have dense morphologies. Films deposited usingTaBr₅ had a step coverage of 0.6, 1 and 1 based on three films analyzed.TaBr₅ based films deposited by PTTCVD generally appeared to be smootherthan the TaF₅ based films deposited by PTTCVD. It is presumed that TaCl₅based films deposited by PTTCVD would have an appearance intermediate tothe TaF₅ and TaBr₅ films, based on experience with other TaN_(x) filmsusing the same precursors.

Selected films were also evaluated by Auger electron spectroscopy. AnAuger analysis spectrum is shown in FIG. 7 with TaBr₅ used as theprecursor for depositing TaN_(x) directly on a Cu surface in a Cu/TiN/Sistack. Analysis of the Auger spectrum confirmed the clean interface andthe minimal diffusion between the Cu and TaN_(x) layers. This suggestedthat little or no attack of the Cu surface occurred during the PTTCVDTaN_(x) deposition. The analysis also confirmed the low level of bromideimpurities present in the film, which was <2 atomic percent as notedfrom Table 3. FIG. 7 also indicated that the TaN_(x) film was N₂ rich(x>1.0), which was consistent with the results shown in Table 3.Nitrogen rich TaN_(x) films (x>1) are expected to have a relatively highelectrical resistivity. TaN_(x) films deposited using TaF₅ as theprecursor appeared the most promising due to their lower resistivity andsmoother microstructure.

Therefore, a method of producing high quality PTTCVD TaN_(x) filmssuitable for integration with IC interconnect elements that contain Cuhas been demonstrated. The method is based on the vapor delivery ofeither TaF₅, TaCl₅ or TaBr₅ precursors. All of the resulting TaN_(x)films demonstrated excellent step coverage, low residual impurityconcentrations, sufficiently high deposition rates and no signs ofTaN_(x) etching of Cu.

It should be understood that the embodiments of the present inventionshown and described in the specification are only preferred embodimentsof the inventors who are skilled in the art and are not limiting in anyway. For example, Ta films may be deposited by PECVD, and TaN films maybe deposited by either thermal CVD alone or plasma enhanced CVD asdisclosed in, respectively, PECVD OF Ta FILMS FROM TANTALUM HALIDEPRECURSORS, THERMAL CVD OF TaN FILMS FROM TANTALUM HALIDE PRECURSORS andPLASMA ENHANCED CVD OF TaN FILMS FROM TANTALUM HALIDE PRECURSORS, all ofwhich are invented by Hautala and Westendorp, assigned to Tokyo ElectronLimited, are copending applications filed on the same date as thepresent application and are expressly incorporated by reference hereinin their entirety. Furthermore, TaN_(x) may be used for plug fillaccording to the invention as disclosed in CVD TaN_(x) PLUG FORMATIONFROM TANTALUM HALIDE PRECURSORS, invented by Hautala and Westendorp andassigned to Tokyo Electron Limited, which is a copending applicationfiled on the same date as the present application and which is expresslyincorporated by reference herein in its entirety. Therefore, variouschanges, modifications or alterations to these embodiments may be madeor resorted to without departing from the spirit of the invention andthe scope of the following claims.

What is claimed is:
 1. A method of depositing a tantalum nitride(TaN_(x)) film on a semiconductor device substrate having a temperaturein the range of about 300° C. to 500° C., the method comprisingproviding a vapor of a tantalum halide precursor selected from the groupconsisting of tantalum pentachloride and tantalum pentafluoride to areaction chamber containing said substrate by heating said precursor toa temperature sufficient to vaporize said precursor, then combining saidvapor with a process gas consisting essentially of nitrogen and one ormore of hydrogen, argon and helium, depositing said TaN_(x) on saidsubstrate by a thermal chemical vapor deposition (CVD) process andplasma treating said deposited TaN_(x) with a hydrogen-containing gas.2. The method of claim 1 further comprising repeating said depositing bythermal CVD and said plasma treating to produce a desired thickness ofsaid film.
 3. The method of claim 2 wherein said substrate includes afeature to be filled and said depositing and said plasma treating arerepeated until said feature is completely filled to thereby form aTaN_(x) plug.
 4. The method of claim 1 wherein said providing of saidvapor includes producing said vapor at a pressure of at least about 3Torr.
 5. The method of claim 4 wherein said precursor is tantalumpentafluoride and said temperature is about 95° C.
 6. The method ofclaim 4 wherein said precursor is tantalum pentachloride and saidtemperature is about 145° C.
 7. The method of claim 1 wherein saidheating of said precursor is to a temperature sufficient to provide avapor pressure of said tantalum halide precursor of at least 3 Torr. 8.The method of claim 1 wherein said delivery of said tantalum halideprecursor in the range of about 1-50 sccm.
 9. The method of claim 1wherein said process gas includes hydrogen gas at a flow of about 0.1-10slm.
 10. The method of claim 1 wherein said process gas is at a flow inthe range of about 0.1-10 slm.
 11. The method of claim 1 wherein saiddepositing occurs at a pressure of said chamber in the range of about0.2-5.0 Torr.
 12. The method of claim 1 wherein said film is integralwith a copper layer of said substrate.
 13. The method of claim 1 whereinsaid TaN_(x) is deposited at a rate of at least about 100 Å/min.
 14. Themethod of claim 1 wherein said substrate comprises an integrated circuitcontaining a high aspect ratio feature.
 15. The method of claim 1wherein said depositing is stopped prior to beginning said plasmatreatment.
 16. The method of claim 15 wherein said depositing is stoppedby halting a flow of said precursor gas and said process gas in saidchamber.
 17. The method of claim 15 wherein said thermal CVD is stoppedby redirecting a flow of said precursor gas and said process gas in saidchamber.
 18. The method of claim 1 wherein said plasma treatment isgenerated by a radiofrequency energy source.
 19. The method of claim 1wherein said tantalum halide precursor is delivered to said reactionchamber without a carrier gas.
 20. The method of claim 1 furthercomprising depositing and treating said TaN_(x) film sequentially with atantalum film.
 21. A method of depositing a tantalum nitride (TaN_(x))film on a semiconductor device substrate having a temperature in therange of about 300° C. to 500° C., the method comprising providing avapor of a tantalum pentafluoride precursor to a reaction chambercontaining said substrate by elevating a temperature of said precursorsufficient to produce a vapor of said precursor to provide a pressure todeliver a tantalum vapor, combining said vapor with a process gasconsisting essentially of nitrogen and hydrogen and optional inertgases, depositing said TaN_(x) on said substrate by a thermal chemicalvapor deposition (CVD) process and plasma treating said depositedTaN_(x) film.
 22. The method of claim 21 further comprising repeatingsaid depositing by thermal CVD and said plasma treating to produce adesired thickness of said film.
 23. The method of claim 21 wherein saidelevated temperature is less than a temperature that would cause areaction between said precursor vapor and said process gas.
 24. Themethod of claim 21 wherein said pressure to deliver said tantalum vaporis at least about 3 Torr.
 25. The method of claim 21 wherein saidelevated temperature is about 95° C.
 26. The method of claim 21 whereinsaid substrate includes a feature to be filled and said depositing andsaid plasma treating are repeated until said feature is completelyfilled to thereby form a TaN_(x) plug.
 27. The method of claim 21wherein said thermal CVD is stopped prior to beginning said plasmatreatment.
 28. A method of depositing a tantalum nitride (TaN_(x)) filmon a semiconductor substrate having a temperature in the range of about300° C. to 500° C., the method comprising providing a vapor of atantalum pentafluoride precursor to a reaction chamber containing saidsubstrate without a carrier gas by elevating a temperature of saidprecursor sufficient to produce a vapor of said precursor, combiningsaid vapor with a process gas consisting essentially of nitrogen andhydrogen and optional inert gases, depositing said TaN_(x) on saidsubstrate by a thermal chemical vapor deposition (CVD) process andplasma treating said deposited TaN_(x).
 29. The method of claim 28wherein said elevated temperature is in the range of about 83° to about95° C.
 30. The method of claim 29 wherein said elevated temperature isabout 95° C.
 31. The method of claim 28 further comprising repeatingsaid depositing by thermal CVD and said plasma treating to produce adesired thickness of said film.
 32. A semiconductor device substratehaving an underlying dielectric layer and comprising a copper (Cu) layerand a tantalum nitride (TaN_(x)) layer wherein said TaN_(x) layer isdeposited by delivering a tantalum halide precursor selected from thegroup consisting of tantalum pentafluoride and tantalum pentachloride toa reaction chamber containing said substrate having a temperature in therange of about 300° C. to 500° C. with said precursor heated to atemperature sufficient to vaporize said precursor, combining said vaporwith a process gas consisting essentially of nitrogen and one or more ofhydrogen, argon, and helium, depositing said TaN_(x) on said substrateby a thermal chemical vapor deposition (CVD) process and plasma treatingsaid deposited TaN_(x) with a hydrogen-containing gas wherein saidTaN_(x) prevents diffusion of said Cu into said underlying dielectriclayer and has less than about 2 atomic percent impurities.
 33. A methodof depositing a tantalum nitride (TaN_(x)) film on a semiconductordevice substrate comprising the steps of (a) providing a vapor of atantalum halide precursor selected from the group consisting of tantalumpentachloride and tantalum pentafluoride to a reaction chambercontaining said substrate having a temperature in the range of about300° C. to 500° C. by heating said precursor to a temperature sufficientto vaporize said precursor, then combining said vapor with a process gasconsisting essentially of nitrogen and hydrogen and optional inertgases, (b) depositing said TaN_(x) on said substrate by a thermalchemical vapor deposition (CVD) process and plasma treating saiddeposited TaN_(x), and (c) repeating steps (a) and (b) to produce adesired thickness of said film.
 34. A method of depositing a tantalumnitride (TaN_(x)) film on a semiconductor device substrate having atemperature in the range of about 300° C. to 500° C., the methodcomprising providing a vapor of a tantalum pentafluoride precursor to areaction chamber containing said substrate by heating said precursor toa temperature of about 95° C. sufficient to vaporize said precursor toprovide a pressure of at least about 3 Torr, then combining said vaporwith a process gas consisting essentially of nitrogen and hydrogen andoptional inert gases, depositing said TaN_(x) on said substrate by athermal chemical vapor deposition (CVD) process and plasma treating saiddeposited TaN_(x).
 35. A method of depositing a tantalum nitride(TaN_(x)) film on a semiconductor device substrate having a temperaturein the range of about 300° C. to 500° C., the method comprisingproviding a vapor of a tantalum pentafloride precursor to a reactionchamber containing said substrate by heating said precursor to atemperature of about 95° C. sufficient to vaporize said precursor toprovide a pressure of at least about 3 Torr, then combining said vaporwith a process gas consisting essentially of nitrogen and hydrogen andoptional inert gases, depositing said TaN_(x) on said substrate by athermal chemical vapor deposition (CVD) process and plasma treating saiddeposited TaN_(x).
 36. A method of depositing a tantalum nitride(TaN_(x)) film on a semiconductor device substrate having a temperaturein the range of about 300° C. to 500° C., the method comprisingproviding a vapor of a tantalum halide precursor selected from the groupconsisting of tantalum pentachloride and tantalum pentafluoride to areaction chamber containing said substrate by heating said precursor toa temperature sufficient to vaporize said precursor, then combining saidvapor with a process gas consisting essentially of nitrogen and hydrogenand optional inert gases, depositing said TaN_(x) on said substrate by athermal chemical vapor deposition (CVD) process, then stopping saiddepositing by halting a flow of said precursor gas and said process gasin said chamber and subsequently plasma treating said deposited TaN_(x).37. A method of depositing a tantalum nitride (TaN_(x)) film on asemiconductor device substrate having a temperature in the range ofabout 300° C. to 500° C., the method comprising providing a vapor of atantalum halide precursor selected from the group consisting of tantalumpentachloride and tantalum pentafluoride to a reaction chambercontaining said substrate by heating said precursor to a temperaturesufficient to vaporize said precursor, then combining said vapor with aprocess gas consisting essentially of nitrogen and hydrogen and optionalinert gases, depositing said TaN_(x) on said substrate by a thermalchemical vapor deposition (CVD) process, then stopping said depositingby redirecting a flow of said precursor gas and said process gas in saidchamber and subsequently plasma treating said deposited TaN_(x).
 38. Amethod of depositing a tantalum nitride (TaN_(x)) film on asemiconductor device substrate having a temperature in the range ofabout 300° C. to 500° C., the method comprising providing a vapor of atantalum halide precursor selected from the group consisting of tantalumpentachloride and tantalum pentafluoride to a reaction chambercontaining said substrate by heating said precursor to a temperaturesufficient to vaporize said precursor, then combining said vapor with aprocess gas consisting essentially of nitrogen and hydrogen and optionalinert gases, depositing said TaN_(x) on said substrate by a thermalchemical vapor deposition (CVD) process and plasma treating saiddeposited TaN_(x), wherein said plasma treatment is generated by aradiofrequency energy source.